The present invention relates to concentrators for concentrating particles of different specific gravities and more particularly to centrifugal concentrators for concentrating minerals such as gold ore from a slurry.
It is common to use centrifugal force to separate out heavier metal ores, such as gold, from lighter material, such as tailings or a slurry comprised largely of sand. This is commonly accomplished using a rotating drum into which the particulate material containing gold is introduced. The gold, having a greater specific gravity than the other particulate material, migrates to the outer layer of the slurry and is removed by various methods. For example, U.S. Pat. No. 585,552 issued June 29, 1897 to Bushby, discloses an ore separator in which the ore is fed into a rotating bowl. Centrifugal force causes the ore to climb the sides of the bowl. At the point of largest diameter of the bowl the particles are stratified, with the precious mineral of high specific gravity nearer the surface of the bowl. Bushby utilizes two adjacent funnels with associated scrapers, arranged at different distances from the axis of rotation, with the first funnel nearest the wall of the bowl, to constantly separate the materials and convey the saved ore to a separate location. Due to the continuous nature of the Bushby separation process, this design fails to provide a sufficiently high concentration of gold in saved material to be commercially feasible for most applications. Also the scraper arrangement is prone to plugging and is subjected to extreme abrasion.
In other devices annular ribs or baffles are provided on the inclined side walls of the rotating drum to collect the heavier mineral particles and thereby provide sufficient yield. In some instances, a supply of mercury would be contained in the rotating drum by flanges to amalgamate gold which collected in it. For example, in the concentrator disclosed in U.S. Pat. No. 4,286,748 issued Sept. 1, 1981 to Bailey, the gold is collected in grooves in the wall of the rotating drum which are defined by annular baffles on the side wall and which impede the migration of the heavier particles up the wall of the drum. From time to time the process is stopped to collect the accumulated gold. The problem with such devices is that the fine particles quickly pack the area of obstruction thus preventing the accumulation of mineral as desired. Various solutions to the problem of packing have been attempted, such as imparting an occilating or bumping movement to the bowl, but none has provided a practical centrifugal concentrator which avoids the problem of packing.